Tutorial: Repair and replacement of Harley-Davidson clutch disks

A little theory

The clutch of a vehicle is the component that connects the engine with the transmission, allowing to connect or disconnect the force (torque) coming from the engine to the transmission, in order to change gears, for example.

It has one or more friction discs, pressed by springs (or a diaphragm) that are released when we press the knob, leaving the engine unconnected with the transmission, what is known as an unplugged motor.

In most motorcycles, the clutch has several friction discs (connected with the engine), interspersed with metal discs (connected to the transmission), all of which are bathed in oil. Friction discs are usually coated with aramid, kevlar, carbon... with the aim of not slipping on metal discs when pressed by springs (clutch engine).

This material wears off over time and can deteriorate due to excess heat, losing its efficiency and allowing the disks to slide between them even under the force of the spring, situation in which we say that the clutch skates.

Diagnosis

We find a motorcycle that when accelerating rises of revolutions, but the speed of the vehicle does not rise in line or, in extreme cases, we gear the first speed and when releasing the lever of the clutch the motorcycle does not advance. In both situations we are likely to have a worn or damaged clutch.

Trick: if we suspect a clutch that starts skating, we can put the bike against a wall and, after putting first speed, accelerate slightly against the wall. The RPM should not go up too much, if they do the clutch is skating.

Changing clutch disks

In this tutorial, we will replace the clutch disks of a Harley-Davidson Sportster. The first thing we will do is drain the oil from the primary crankcase (in this model it contains both the primary oil and the transmission oil)

and loosen the primary chain tensor.

After releasing the rest bracket and shift lever, with the help of a Torx 27 key, let's loosen the clutch cover screws, allowing us to access the ramp mechanism. With a flat screwdriver let's loosen this mechanism until we release the ramp, which we can extract.

We continue releasing all the screws that hold the cover of the primary chain and then we can separate it from the crankcase.

The next step requires the use of a clutch spring compressor, a specific utility for the year and model of the vehicle in which we are going to work, and which will allow us to compress the diaphragm (spring) in order to release the circlip that holds it.

With the help of a pair of fine screwdrivers or hooks, we remove the clutch discs one by one while checking and cleaning everything.

Improving the original

A special feature of some Sportster models is that they have 8 friction plates and 6 steel discs, and located in the middle, a double riveted disc that serves to smooth the operation. This disc is usually broken very easily, destroying the other components of the clutch.

To prevent this problem and at the same time increase the efficiency of the clutch, we will install an "extra plate" kit from the American manufacturer Barnett, which eliminates this spring disc and replaces it with two more disks, increasing the friction surface by 12%, improving both the grip and the duration of the components.

Similarly, we will replace the small release bearing, which is the one that supports all the pressure when the engine is unplugged. This is a very economical component that should be replaced with each change of disks.

Assembly

After having had the friction discs a couple of hours submerged in oil, we started by installing one of these, followed by a metal disc. We reinstall another friction disc, a metallic one... and let's intercalate them like this until they're all in place.

We re-position the pressure plate and its circlip, and we can now release the spring compression tool. At this moment we use to extract the disembarkation mechanism

and change the bearing for a new one, we will help with a bearing installer and a press or bench screw.

We can now put a new joint and reposition the clutch cover, careful not to damage the gear shift lever shaft seal. This seal is recommended to be new, so we will use a complete primary joint kit when performing this type of operation.

Screw the lid in order and to the torque indicated in the service manual of the year and model of the motorcycle we are working with (remember to consult the manual, it is the most important tool). After fully compressing the clutch cable tensioner, we reinstall the ramp mechanism and mount the clutch cover instead.

In this step we can fill with oil, the Sportster model uses 1 quart (946mL) of oil specific for primary and transmission.

Next, we tense the primary chain again and install the inspection cover by tightening the screws to their corresponding pair (all these procedures are detailed in the manual corresponding to each model).

We only have to adjust the clutch cable tensioner, to do this we will extend the adjuster until the cable has a roughly 3mm clearance.

This clearance is necessary to allow the expansion of the clutch components when dilated by heat, if we do not leave it the clutch discs will burn prematurely.

Shooting

After the assembly we have to perform a test lap, verifying the correct operation of the clutch and the absence of oil leaks. It is advisable to make a small "rolling" of the clutch, without accelerations or sudden decelerations in the first kilometers, so that the components settle correctly, thus prolonging the useful life of the same.

Frank Burguera

#mecanicaharley